Anisotropic FMR‐linewidth of triple‐domain Fe layers on hexagonal GaN(0001)

Abstract We present a ferromagnetic resonance (FMR) study of Fe films with thicknesses between 5 and 70 nm prepared by electron‐beam evaporation on top of hexagonal GaN(0001). X‐ray diffraction (XRD) and low‐energy electron diffraction (LEED) suggest the growth in crystallographic Fe(110) domains with three different orientations. The magnetic properties have been investigated by in‐plane angle‐dependent FMR at frequencies between 4.5 to 24 GHz. All samples show a hexagonal in‐plane anisotropy with the easy axes oriented parallel to the Fe [001] directions. The anisotropy field strength of about 8 mT reveals a bulk‐like thickness dependence. Therefore, we can exclude the following origins of anisotropy: (i) interface effects because of the bulk‐like thickness dependence and (ii) averaged first order cubic or uniaxial anisotropies arising from the three grain orientations because of the relative strengths. We qualitatively explain the sixfold anisotropy by spin relaxation inside the grains. The FMR linewidth versus frequency curves are linear with almost no zero‐frequency offset indicating a good homogeneity of the magnetic properties over the sample area. However, the effective damping parameter α shows pronounced anisotropy and thickness dependence, with enhanced damping along the hard axes and for thicker layers. We suggest that the additional damping can be explained by two‐magnon scattering at defects which are due to the triple domain structure. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)